Modular growth of a wireless network base station's voice or data-carrying capability often involves adding both more RF (radio frequency) transmit power as well as more RF bandwidth for transmission and reception. Designing a cost effective radio transceiver that can be easily scaled to support both low power and a low number of RF carriers, as well as allowing for the addition of both power and carriers, can be difficult. In order to reduce costs, narrower band transmitters and receivers are oftentimes designed and utilized, rather than wideband transmitters and receivers that are more easily scaled.
Often, a single radio transceiver may include two receivers in the reverse link band for reception diversity, plus a single transmitter for forward link transmissions, with no provisions for transmit diversity. Older designs (e.g., analog FM, TDMA, and GSM) would add capacity by adding many parallel transceivers per sector. This requires either low power combining before a single high power multi-carrier linear amplifier (e.g., a feed-forward amplifier), a separate power amplifier for each RF carrier followed by a multiplexer combiner filter (e.g., a tunable cavity type RF filter), or separate transmit antennas for each carrier. Alternatively, more expensive multi-carrier transceivers may be used to support growth for wideband spread spectrum-type air interfaces such as UMTS or CDMA (code division multiple access). These devices are more costly in that they support wider bandwidths to begin with, and only become cost effective after capacity is added and the transmitted carriers occupy more of the RF bandwidth. Often, the transmitter portion supports multi-carrier transmission because post amplification high power combining is neither feasible nor cost effective for wideband CDMA-type signals where it is difficult to build cavity type combiners for such wide carriers bandwidths, and where using multiple transmit antennas is cost prohibitive.